Wireless communication systems are widely spread all over the world to provide various types of communication services such as voice or data. In general, the wireless communication system is a multiple access system capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, etc.). Examples of the multiple access system include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, etc.
While having almost the same complexity as the OFDMA, SC-FDMA has a lower peak-to-average power ratio (PAPR) due to a single carrier property. Since the low PAPR is advantageous for a user equipment (UE) in terms of transmission power efficiency, the SC-FDMA is adopted for uplink transmission in a 3rd generation partnership project (3GPP) long term evolution (LTE) as disclosed in section 5 of the 3GPP TS 36.211 V8.2.0 (2008-03) “Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 8)”.
In a typical wireless communication system, one radio frequency (RF) is considered in general even if a bandwidth is differently set between an uplink and a downlink. The RF is used to upconvert a baseband signal. The RF may be referred to as another terminology, such as carrier frequency, center frequency, component carrier, etc. In the 3GPP LTE, the number of RFs constituting the uplink or the downlink is 1, and the bandwidth of the uplink is symmetrical to the bandwidth of the downlink. However, except for some areas of the world, it is difficult to allocate frequencies of wide bandwidths. As a technique for effectively using fragmented small RFs, a spectrum aggregation (also referred to as bandwidth aggregation or carrier aggregation) technique is being developed to obtain the same effect as when a frequency band of a logically wide bandwidth is used by aggregating a plurality of physically non-contiguous RFs in a frequency domain. The spectrum aggregation includes a technique for supporting a system bandwidth of 100 mega Hertz (MHz) by using multiple RFs even through, for example, the 3GPP LTE supports a bandwidth of up to 20 MHz, and a technique for allocating an asymmetric bandwidth between the uplink and the downlink. The multi-RF system is introduced to support an increasing throughput, to avoid cost increase due to the introduction of a broadband RF device, and to ensure compatibility with a legacy system.
Accordingly, there is a need for a method of effectively transmitting data in a multi-RF system.